Flamethrower

The Flamethrower is a ranged weapon which uses Hydrogen gas as its fuel. It is fairly effective against mobs as it deals damage when they are directly hit with the stream and sets them on fire. It is most effective on large groups of mobs, where the user can hose down the entire group with fuel at a short distance.

Modes

You can switch between three fire modes using Shift + Item Mode (default M). The modes are

Combat - The default mode. Damages mobs and sets them on fire. Destroys any items on the ground. Does not set fire to blocks nor damage them.

Heat - Same as combat, but blocks/items that have a smelter recipe will be instantly converted into it. For example you can fire a short burst at iron ore block and a single ingot of iron will be dropped.1

Inferno - Same as combat, but blocks that the stream hits will be hit with blast damage (like with creepers, ghasts, TNT) and will usually be destroyed. Nearby blocks will be set on fire.

1 Items that can be cooked multiple times are usually in their final form. For example, the Big Reactors mod has a smelter recipe for charcoal that cooks them into a graphite bar. So, if you fire a Heat stream at a log you'll likely end up with the graphite bar instead of the charcoal.

Tips

You can damage mobs that are in water with the flamethrower stream, but not if you are underwater, and the mobs won't be set on fire for more than a tick.

The range is short, having a maximum range of about 16 blocks.

The stream moves slowly, so it's more effective when kiting (firing while moving backwards or strafing left/right).

Although you'll appear to set yourself on firing when moving forwards while firing, you won't be damaged by your fire stream.